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Cisco Internetwork Operating System (IOS) has been around since a little after the inception of Cisco Systems as a company. In 1984, Len and Sandy Bosack from Stanford University founded Cisco Systems with a small commercial gateway server. The first Cisco router that I touched was an Advanced Gateway Server (AGS), which was the first marketed product of the company. After this came the Mid-Range Gateway Server (MGS), the Compact Gateway Server (CGS) and later the Integrated Gateway Server (IGS) and AGS+. The first version of IOS that I touched was 8.2(7). The operating system was based on a Unix-based system and was designed as a monolithic operating system, meaning that processes are stacked and interrelated.
Now that we are moving towards IPv6, the logical move would be to also run OSPF for that protocol suite, which makes sense and reduces the learning curve for implementation and support. But, that would mean that you have to run two OSPF processes — one for IPv4 unicast and one for IPv6 unicast. That means two sets of policies have to be applied, including security for OSPF itself. Running OSPFv3 for both IPv4 and IPv6 reduces the number routing protocols and the configuration that goes with that. It makes it easier to implement policy in a consistent way for both protocol suites.
What is PBR? Policy-Based Routin (PBR) is the process of using a route map to match on something more than the destination and then defining the path out of the router based on those conditions. PBR could match on destination only, but typically we would match on more. PBR is considered to be an exception to the RIB and is looked at before examining the RIB.
As I’ve stated before, I like Border Gateway Protocol (BGP). I think it’s an interesting protocol, and yes — it’s complicated, but I guess that part of why I like it. There are a lot of knobs to tweak in BGP, maybe too many, but that’s another post. Anyway, we are now running BGP version 4 and it has had extensions written that support more than just IPv4 unicast routing. We now have IPv4 multicast, IPv6 unicast and multicast, VPNv4, VPNv6, and a few others.
Where should you apply the CSS, and why are there two places to apply it? One approach is to pick one of the parameters and apply the permissions there. Quite often, an administrator will pick the phone-level CSS and configure it there so that it applies to all calls made from all lines. The goal is to specify what partitions are allowed to be called.
For smaller companies, configuring a dial plan to account for variations in dialed numbers is often not a problem. However, companies that are larger and more global in nature encounter a number of issues when designing their dial plan approach.
Border Gateway Protocol (BGP) is a fascinating protocol because there are a lot of things that can be done with BGP. However, there has always been an issue with BGP, which is convergence (the time the network or protocol takes to accept change). BGP was designed for scale, not speed, so it’s something that we’ve had to tolerate from its inception.
License provisioning has always been a bit of a challenge in the CUCM environment. Prior to CUCM v9.0, licensing was managed on a per-cluster basis with each cluster requiring its own license files that were tied to the media access control (MAC) address of the cluster’s publisher. This approach to license management was limiting in the fact that one cluster might have unused licenses while another cluster may be at its limit and sharing between clusters was not possible.
Occasionally I am asked to configure the ability to block calls based on Caller ID. Prior to Cisco Unified Communications Manager (CUCM) v8, the only way to block these calls was to configure voice translation rules and profiles on the gateway receiving the calls. This has changed in CUCM v8 with the introduction of an additional parameter in translation patterns: Route Next Hop By Calling Party Number.
While most organizations have not yet fully (or in many cases even partially) adopted cloud computing, the trend is growing in all but the smallest businesses.